Fractionation of mixtures of aromatic hydrocarbons



2,917,562 Patented Dec. 15, 1959 FRACTIONATION OF MIXTURES OF AROMATIC HYDROCARBONS Glen C. Tempieman, Findlay, Richard D. Morin, C-

lumbus, and Robert A. Ewing, Worthington, Ohio, assignors, by direct and rnesne assignments, to The Ohio Oil ornpany, Findlay, Ohio, a corporation of Ohio I No Drawing. Application February 20, 1956. Serial No. 566,393

5 Claims. (Cl. 260-674) This invention relates to the treatment of a mixture of aromatic hydrocarbons to separate therefrom fractions with compositions different from the composition of the initial mixture. Further, this invention relates to the fractionation of mixtures of aromatic hydrocarbons having various boiling points whereby substantial separation of fractions of higher-boilingpoint aromatic hydrocarbons from lower-boiling-point aromatic hydrocarbons is effected. This invention further relates to the separation of aliphatically substituted aromatic hydrocarbons, such as long-chain alkyl-substituted aromatic compounds, from aromatic compounds containing shorter chain hydrocarbon substituents and from unsubstituted aromatic compounds.

In copending application Serial No. 464,518 filed October 25, 1954, there is disclosed a process for the separation of aromatic hydrocarbons from nonaromatic hydrocarbons whereby an extract is obtained substantially enriched in aromatic content as compared to the initial mixture of aromatic and nonaromatic compounds. The process is based upon the discovery of the selective solvent action of certain gamma lactones for aromatic hydrocarbons in preference to nonaromatic hydrocarbons. The disclosed gamma lactones exhibiting such preferential selectivity for aromatic hydrocarbons over nonaromatic hydrocarbons are the lactones of the saturated and unsaturated gamma-hydroxy butanoic acids and the methyl-substituted lactones of these acids. Specific examples representative of the gamma lactones are gamma butyrolactone, gamma methyl-gamma butyrolactone (gamma valerolactone) and gamma butenolactone (gamma crotonolactone). It has now been found that the capacity of these gamma lactones for aromatic hydrocarbons can be altered so as to selec tively obtain different fractions of aromatic hydrocarbons from mixtures of aromatic hydrocarbons. This can be accomplished by the addition of controlled amounts of water to the solution of the mixture of aromatic hydrocarbons in the gamma-lactone solvent. Unexpectedly, the fractions of aromatic hydrocarbons separated by the process of this invention are not equivalent to each other compositionwise. The composition of the fractions separable differ from each other in the nature of the aromatic compounds in the fractions and in the proportions in which they initially existed in the aromatic hydrocarbon mixture. Thus, in the treatment of a mixture of aromatic hydrocarbons, the individual components of which have boiling points over a wide range, it is possible to obtain substantially complete separation of the higher-boiling-point aromatic hydrocarbons from the lower-boiling-point aromatic hydrocarbons in the mitxure. Further, by the process of this invention, it is possible to obtain substantially complete separation of high-molecular-Weight aromatic hydrocarbons and high-molecular-weight aliphatically substituted aromatic hydrocarbons from low-molecular-weight aromatic hydrocarbons and lowmolecular-weight aliphatically substituted aromatic hydrocarbons.

In general, the process is carried out by first obtaining a solution of the mixture of aromatic hydrocarbons in the gamma-lactone solvent. Ideally, such solution exists in the gamma-lactone extract phase resulting from the extraction of petroleum reformate by the process of said copending application Serial No. 464,518, whereby separation of aromatics from nonaromatics in the reformate is obtained, yielding an extract substantially enriched in aromatic hydrocarbons. A controlled amount of water, preferably from about 20 to 50 percent by volume of the extract, is added to the extract phase. The water is intimately contacted with the extract phase. Upon standing, there is separated an immiscible hydrocarbon fraction containing substantially all of the higher boiling point aromatics from the extract phase. The lower aqueous lactone phase is separated from the immiscible hydrocarbon fraction. The lower-boiling-point aromatics remaining in the separated aqueous lactone phase may be recovered therefrom, preferably by subjecting the aqueous lactone phase to distillation to yield overhead water and low-boiling point aromatic hydrocarbons. Alternatively, instead of recovering the aromatic fraction remaining in the separated aqueous lactone phase by distillation, additional water may be added to the aqueous lactone phase in sufiicient quantity to liberate the lower-boiling-point aromatic hydrocarbon fraction. The latter fraction may then be separated from the residual aqueous lactone phase. The lactone may be recovered for reuse by distillation of the water therefrom. In the case of fractionating the aromatic hydrocarbons contained in the extract of the petroleum reformate, the lower-boiling-point aromatic hydrocarbon fraction consists principally of low-molecular-weight aromatic hydrocarbons such as benzene, methyl-substituted benzenes, such as toluene, xylenes, trimethyl benzenes, and may also contain short-chain alkyl homologues of methyl-substituted benzenes. Thus, from a petroleum reformate aromatic extract which contains aromatic hydrocarbons boiling in the range of from approximately F. to 455 F., it is possible to fractionate therefrom the higherboiling-point hydrocarbons from the lower-boiling-point hydrocarbons.

The following examples illustrate the invention in more detail. For purposes of illustration, the mixture of aromatic hydrocarbons in each example is a mixture of aromatic compounds extracted from the nonaromatic hydrocarbons in petroleum reformate by the use of the gamma-lactone solvents of copending application Serial No. 464,518.

EXAMPLE I A gamma-butyrolactone extract rich in aromatic hydrocarbons was obtained by extracting petroleum reformate with gamma butyrolactone, the ratio of the lactone to the reformate being approximately 1:1 by volume. This extract phase contained a rich mixture of aromatic compounds including mononuclear aromatic compounds and aliphatic-substituted mononuclear aromatic compounds such as benzene, methyl-substituted benzenes, and higher alkyl-substituted benzenes in addition to polynuclear and aliphatic-substituted polynuclear compounds such as naphthalene and methyl naphthalenes. This butyrolactone extract phase rich in aromatics was intimately contacted with water in the volume ratio of about one part water to two parts of the extract phase. Upon standing, a hydrocarbon fraction separated from the aqueous lactone phase. The lower aqueous butyrolactone phase, immiscible with the water-sprung hydrocarbon Distillation analysis A gamma-butyrolactone extract rich inaromatichydrocarbons was obtained by extractingpetroleumreformate with gamma butyrolactone containing about 1 .percent water by volume, the ratio of thelactoneto thereformate being approximately 1.5 :1 by volume. This .extr actphase, which contained a rich mixture of aromatic compounds as in Example I, was intimately contacted with water in the ratio of 0.2.part of water .to 1 part of the extract phase. Upon. standing, an immiscible hydrocarbon fraction. separated from the aqueous lactone phase. The lower aqueous lactonephase was withdrawnv and distilled at temperatures up to the boilingpoint of the butyrolactoneto .yield overhead anaqueousdistillate from .which separated .an aromatic hydrocarbon fraction. This distilled aromatic hydrocarbon fraction was subjected to a distillation analysis.

Distillation analysis Component: Percent Benzene 1 Toluene 20 Xylene 32 Trimethyl benzenes V 24 .Higher alkyl-benzenes 23 Boiling range F. 187-428 Calculated average molecular vweight 114 Specific gravity (25 C.) 0.860

Refractive index (25 .C.) 1.4937

The end boiling point of the combined water-sprung EXAMPLE III A gamma-butyrolactone extract rich in aromatic hydrocarbons was similarly obtained as in the previous examples using gamma butyrolactone containing 1 percent of water, the volume ratio of the lactone to reformate being approximately 2:1. The gamma-lactone extract phase rich in aromatics was then intimately mixed with Water in the volume ratio of 0.2 part water to 1 part of the extract phase. Theaddition of the water springs a higher boiling hydrocarbon fraction from the lactone phase. The aqueous lactone phase, immiscible with the water-sprung hydrocarbon fraction, was withdrawn and subjected to distillation at'temperatures up to the boiling point of the butyrolactone to yield overhead water and an aromatic hydrocarbon fraction. A distillation analysis waslmade uponlthisdistilled aromatic fraction.

Distillation analysis Component: Percent Benzene 1 Toluene 20 Xylene 39 Trimethyl benzenes 27 Higher alkyl benzenes 13 Boiling range R. 176-360 Calculated average molecular weight Specific gravity (25 C.) 0.860 Refractive index (25 C.) 1.4930

The end point of the boiling range for the combined water-sprung aromatichydrocarbon fraction and the distillated aromatic hydrocarbon fraction was about 444 F. The refractive index (25 C.) for the combined watersprung and distilled aromatic hydrocarbon fraction was 1.47.82.

The examples disclose that by the addition of various amounts of water it is possible to selectively alter capacity of the gamma-lactone solvents. In general, for the higher-boiling-point aromatics and high-molecularweight aromatics, the saturation point has been found to be lowered to a greater degree with smaller amounts of water than the saturation point for the low-boiling-point and low-molecular-weight aromatic hydrocarbons. 'Although successive additions of incremental amounts of water to the gamma-lactone solution of the mixture of aromatic hydrocarbons progressively springs more hydrocarbons from solution, the effective minimum amount of water to spring the high boiling aromatics from the soldtion is about 20 percent by volume based on the volume of the-lactone-aromatic solution. This quantity of water springs about two-thirds of the aromatics and only traces of the remainder are retained in the butyrolactone after distillation of the aqueous lactone phase to recover the lactone therefrom. The addition of about 50 percent by volume of water based on the lactone-aromatic phase is a practical maximum since, with this amount of water, saturation appears to be of the order of about 2 percent aromatics.

The distilled aromatic hydrocarbon fraction from the lactone extract phase from petroleum reformate is a valuable fraction since it contains benzene, toluene, and xylene. By redistillation of this fraction, high-quality toluene and xylene fractions may be obtained in yields of about 3.0 and 4.8 percent, respectively, of the starting reformate. While this process finds particular adaptability to the fractionation of mixtures of aromatic hydrocarbons obtainable from petroleum reformate, the process is also applicable to other mixtures of widely variant aromatic compounds.

The above description and examples have-been given for illustration of the invention and not for the purpose of limiting the invention specifically to the disclosure therein. Many modifications and variations of the invention asherein set forth may be made without departing from the spirit or scope thereof. Therefore, only such limitations should be imposed as are indicated in the following claims.

What is claimed is:

1. The process of fractionating a mixture of aromatic hydrocarbons containing benzene, methyl-substituted benzenes, short-chain alkyl homologues of saidrnethyl benzenes, and other high-molecular-weight aromatic hydrocarbons comprising: (a) dissolving said mixture of aromatic hydrocarbons in at least one gamma lactone selected from the group consisting of the lactoneof the saturated and unsaturated gamma-hydroxybutanoic ac ds and the methyl-substituted lactones of said acidsyand (b) adding-,onlyasmuch water to the resultingsolution as is necessary. to separate therefrom an immiscible fraction of;aromatichydrocarbons. other than the benzene,

methyl-substituted benzenes, and short-chain alkyl homologues of said methyl-substituted benzenes.

2. The process of fractionating a mixture of aromatic hydrocarbons containing benzene, methyl-substituted benzenes, short-chain alkyl homologues of said methyl benzenes, and other high-molecular-weight aromatic hydrocarbons comprising: (a) dissolving said mixture of aromatic hydrocarbons in at least one gamma lactone selected from the group consisting of the lactone of the saturated and unsaturated gamma-hydroxy butanoic acids and the methyl-substituted lactones of said acids; (b) adding water to the resulting solution to separate therefrom an immiscible fraction of aromatic hydrocarbons other than the benzene, methyl-substituted benzenes, and short-chain alkyl homologues of said methyl-substituted benzenes; (c) removing said immiscible fraction from the resulting aqueous gamma-lactone solution; and (d) recovering from said aqueous gamma-lactone solution an aromatic hydrocarbon fraction containing substantially all of the benzene, methyl-substituted benzenes 20 and the short-chain alkyl homologues of said methyl benzene.

3. The process of claim 1 wherein the water is added to the gamma-lactone solution of the mixture of aromatic hydrocarbons in an amount of about 20 to 50 percent by volume based on the volume of said gamma-lactone solution.

4. The process of claim 2 wherein the water is added to the resulting solution in an amount of from about 20 to 50 percent by volume based on the volume of said gamma-lactone solution.

5. The process of claim 1 wherein the gamma lactone is gamma butyrolactone.

References Cited in the file of this patent UNITED STATES PATENTS 

1. THE PROCESS OF FRACTIONATING A MIXTURE OF AROMATIC HYDROCARBONS CONTAINING BENZENE, METHYL-SUBSTITUTED BENZENES, SHORT-CHAIN ALKYL HOMOLOGUES OF SAID METHYL BENZENES, AND OTHER HIGH-MOLECULAR-WEIGHT AROMATIC HYDROCARBONS COMPRISING: (A) DISSOLVING SAID MIXTURE OF AROMATIC HYDROCARBONS IN AT LEAST ONE GAMMA LACTONE SELECTED FROM THE GROUP CONSISTING OF THE LACTONE OF THE SATURATED AND UNSATURATED GAMMA-HYDROXY BUTANOIC ACIDS AND THE METHYL-SUBSTITUTED LACTONES OF SAID ACIDS; AND (B) ADDING ONLY AS MUCH WATER TO THE RESULTING SOLUTION AS IS NECESSARY TO SEPARATE THEREFROM AN IMMISCIBLE FRACTION OF AROMATIC HYDROCARBONS OTHER THAN THE BENZENE, METHYL-SUBSTITUTED BENZENES, AND SHORT-CHAIN ALKYL HOMOLOGUES OF SAID METHYL-SUBSTITUTED BENZENES. 